Fragility Curve Development for Assessing Midrise Steel Building with Buckling Resistant Braced System Having Vertical Irregularity

In this paper, the fragility curves have been developed for assessing vertically irregular midrise steel building with Buckling Resistant Braced (BRB) system. The effect of different vertical irregularities of mass, stiffness and the concurrent variation of stiffness and strength was investigated in the seismic response of a ten-story steel building. The fragility curves of both the regular and irregular structures were developed through the incremental dynamic analysis and the effects of vertical irregularities were evaluated in the seismic performance of the structure. Fragility curves show that among all the vertical irregularities, variation in the mass has little effect on the probability exceedance of demand from capacity. Meanwhile, the concurrent variation of stiffness and strength shows a significant increase in the probability exceedance of demand from capacity, especially through the nonlinear phase of structural behavior, through the collapse prevention to the global instability limit states.